| Objective:To investigate the effect of arctigenin(AG)on depression-like behavior induced by Toxoplasma gondii(T.gondii)infection in mice by establishing a mouse model of infection with the T.gondii RH strain.In vivo and in vitro experiments were carried out to further investigate the mechanism of AG on the depression-like behavior induced by T.gondii infection in mice.It provides scientific basis for the treatment of neuropsychiatric diseases induced by T.gondii infection.Methods:(1)In vivo experiment,BALB/c mice were randomly divided into four groups and then i.p.injected with 1 × 105 tachyzoites of the T.gondii RH strain.After 4 h of infection,each group of mice were orally treated with different drugs,i.e.,0.5%CMC-Na(model group),100 mg/kg AG(AG group),100 mg/kg SD-Na(SD-Na group),respectively,once a day for 6 days.Normal control group was neither infected nor treated.On the sixth day after infection,sucrose preference experiment,tail suspension experiment and forced swimming experiment were carried out respectively,and brain tissue and serum were extracted from the mice in each group.(2)The contents of 5-hydroxytryptamine,dopamine and IDO in serum and brain tissues of mice were determined by ELISA.Western blot was used to detect the expression of SAG1,Iba-1,IFN-γ,TNF-α,iNOS,TLR4,TRIF,p-NF-κB p65,NF-κB p65,p-IκBακ and IκBα proteins in mouse brain tissues.(3)In vitro experiment,MTS assay was used to determine the safe concentration of AG on BV2 cells.BV2 cells were divided into the normal group,the model group,the AG high-dose group,the AG low-dose group and the SD group.After the RH strain was infected with a cell dose of 5 times,the cells were treated with dimethyl sulfoxide,AG(20 μM,5 μM)and SD(100 μg/mL)in addition to the normal group,and cell precipitation was collected.(4)mRNA expression levels of SAG1 and T.g.HSP70 in BV2 cells were detected by RT-PCR.The protein expression of Iba-1,IFN-γ,TNF-α,iNOS,TLR4,TRIF,p-NF-κB,NF-κB p65,p-IκBα and IκBa in BV2 cells were measured by western blot analysis.Immunofluorescence assay was used to detect Iba-1 and NF-κB p65 nuclear expression in BV2 cells.Results:(1)Acute T.gondii infection induced depression-like behaviors in mice and induced IDO and neurotransmitter disorders,while AG treatment significantly improved depression-like behaviors in infected mice,inhibited the high expression of IDO,and significantly improved neurotransmitter disorders.(2)T.gondii infection induced increased expression of toxoplasma specific gene SAG1 or T.g.HSP70 in brain tissues and BV2 cells,and AG significantly inhibited the expression of SAG1 or T.g.HSP70.(3)The expressions of Iba-1,IFN-γ,TNF-α,iNOS,TLR4,TRIF,p-NF-κB p65 and p-IκBα protein were up-regulated and the expressions of NF-κB p65 and IκBα protein were down-regulated in the brain tissues of mice induced by T.gondii infection.The expression of these proteins was significantly inhibited after AG treatment.(4)The expressions of Iba-1,IFN-γ,TNF-α,iNOS,TLR4,TRIF,p-NF-κB p65 and p-IκBα protein were up-regulated and the expressions of NF-κB p65 and IκBa protein were down-regulated in the BV2 cells induced by T.gondii infection.The expression of these proteins was significantly inhibited after AG treatment.(5)Immunofluorescence assay results showed that the expression of Iba-1 was increased in BV2 cells induced by T.gondii infection,and the nuclear translocation of NF-κB p65 was induced.However the expression of Iba-1 and NF-κB p65 nuclear translocation were significantly inhibited by AG.Conclusion:AG inhibits the depression-like behaviors of mice induced by T.gondii infection by reducing the proliferation of T.gondii in microglia cells.In addition,AG inhibited the activation of TLR4/NF-κB signaling pathway in microglia,inhibited the occurrence of neuroinflammatory response induced by overactivation of microglia,and inhibited the depression-like behaviors induced by T.gondii infection in mice.It indicates that AG has potential value in treating neuropsychiatric diseases induced by T.gondii infection. |
